An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri - Paris Observatory

1) The portion of a shadow in which light from an extended source is partially but
not completely cut off by an intervening body; the area of partial shadow surrounding
the umbra.
2) The lighter part of a shadow during an eclipse. An observer standing in the penumbra of a
Solar eclipse will see a partial eclipse.
3) The lighter zone surrounding the dark area (→ umbra)
of a → sunspot. It consists of fine, light filaments
which are approximately radial for sunspots with circular outline, but irregular
for complex spots.

A lunar eclipse that
occurs when the Moon passes through the Earth's → penumbra,
but misses the darker umbral shadow. Because the Moon is only partially
dimmed, a penumbral eclipse is not impressive. Total
penumbral eclipses are rare, and when these occur, that portion of the
Moon which is closest to the umbra can appear somewhat darker than the
rest of the Moon.